The Solution to Leetcode 118 Pascal's Triangle

Question:

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,

Return

[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]

思路：由上述例子可以看出，元素之间满足这样的一个关系：a[i][j]=a[i-1][j-1]+a[i-1][j]，除了每一行的第一个数和最后一个数都是1以外。
Answer:

class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector< vector<int> >a(numRows,vector<int>(numRows));
int i=0;
int j=0;
for(i=0;i<numRows;i++)
{
a[i].resize(i + 1);
for(j=0;j<=i;j++)
{
if (j==0||j==i)
a[i][j]=1;
else
a[i][j]=a[i-1][j-1]+a[i-1][j];
}
}
return a;

}
};

run code results:


Your input

5

Your answer

[[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Expected answer

[[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]